1. Field of the invention
The present invention relates to a shock absorption device and a control method thereof for a small swing radius excavator, which can relieve shock generated on a boom cylinder when a boom of the excavator ascends at its maximum height through manipulation of a control level by controlling the flow rate of hydraulic pumps, being supplied to the boom cylinder, and thus can secure the stability of the excavator.
2. Description of the Prior Art
Generally, a swing excavator is classified into a standard swing excavator and a small swing radius (SSR) excavator.
In the standard swing excavator, if an upper swing structure has a posture directed to a forward/backward direction against a lower driving structure (i.e. if a working device has a posture directed to the traveling direction of the lower driving structure), a rear end part of the upper swing structure projects to an outside so as to be longer than a front/rear part of the lower driving structure (i.e. an end part in a traveling direction). If the upper swing structure has a posture directed to a horizontal direction against the lower driving structure (i.e. if the working device has a posture directed to a direction perpendicular to the traveling direction of the lower driving structure), the rear end part of the upper swing structure projects to an outside so as to be longer than a left/right part of the lower driving structure (i.e. an end part in a direction perpendicular to the traveling direction).
Accordingly, since a distance from the rear end part of the upper swing structure to the swing center thereof is long and the rotational moment of the rear part of the upper swing structure becomes high, it is difficult that the rotational moment of the front part of the upper swing structure that is generated by the excavation force of the working device causes the overturning of the excavator. Accordingly, the excavator can provide a large excavation force, and thus the workability is improved.
As illustrated in FIG. 1, in the small swing radius (SSR) excavator, if the upper swing structure 2 has a posture directed to a forward/backward direction against the lower driving structure 1, the rear end part of the upper swing structure 2 is included in the front/rear part of the lower driving structure 1. If the upper swing structure 2 has a posture directed to the horizontal direction against the lower driving structure 1, the rear end part of the upper swing structure 2 is included in the left/right part of the lower driving structure 1.
In the drawing, unexplained reference numeral A denotes a working device, such as a boom, an arm, or a bucket, which is driven by a hydraulic cylinder, and B denotes a cab mounted on the upper swing structure 2.
Accordingly, since the rear end part of the upper swing structure 2 is included in the front/rear part and the left/right parts of the lower driving structure 1, it does not interfere with an obstacle near the lower driving structure 1, so that the stability is secured during the swing operation, and the operator's swing manipulation becomes excellent. Even if an obstacle exists near the lower driving structure 1, the upper swing structure 2 can perform the swing operation, and this facilitates the work in a narrow space.
In this case, the terms “front/rear part” and “left/right part” mean the direction or side based on the operator in the cab.
In order to reduce the swing radius of the working device, the swing excavator is provided with a boom cylinder having a length that is much larger than the length of a standard type excavator to extend the maximum angle of a boom. If the boom cylinder reaches the stroke end and is abruptly stopped while the boom cylinder is driven to make the boom ascend at its maximum height, shock is generated when the boom cylinder becomes in contact with a cushion plunger, and the endurance of the corresponding parts is lowered to shorten the life span thereof. Also, due to the cause in shape of the boom cylinder and the boom in the corresponding position, the stability of the equipment is lowered by such an abrupt stop of the boom cylinder.
In order to prevent the shock generation when the boom ascends at its maximum height, a proximity sensor for detecting the rotation angle of the boom cylinder may be installed in a specified position of the boom cylinder, and a separate driving device may be used to control the main control valve so that the main control valve controls the hydraulic fluid being supplied to the boom cylinder in accordance with the detection signal from the proximity sensor. In this case, however, the structure of the hydraulic circuit is complicated due to the increase of the corresponding parts, and thus the manufacturing cost is increased.